The present invention relates to an evaluation device for neutralizing interference components of a measuring signal at the output of a lambda probe arranged in. an exhaust gas outlet of an internal combustion engine.
The measuring signal of a lambda probe depends on a plurality of magnitudes, particularly on the oxygen concentration in exhaust gas to be determined, and also on temperature and counterpressure of the exhaust gas. The following disclosure is concerned with the elimination of the effects of the exhaust gas pressure.
The influence of the pressure fluctuations on the measuring signal depends on the type of lambda probe and accordingly the measuring output signal of the probe exhibits considerable deviations from its correct value.
Conventional evaluation devices for the measuring signal from lambda probes includes a low-pass filter for filtering fast interference signals, and a A/D converter which is sampled after each program cycle of the device. The integration time period of the low-pass filter must not be selected too long lest the reaction at the output of the A/D converter on the changes of the actual lambda value be too sluggish. Consequently, interference components due to the pressure variations are not filtered out and the output signal determined at sampling time points may deviate upwards or downwards from the actual lambda value. Accordingly, the regulating device into which the sampled output signal is supplied, contains erroneous actual value data which prevent an optimum regulating result.